*2.1.1 Solar drying*

Sun is as old as the universe itself and is an inexhaustible and free source of energy, utilized for drying of banana since ancient times. Solar drying can be classified into direct and indirect methods of drying.

## *2.1.2 Direct method*

This is a traditional method which involves the sunlight to dry banana. Banana to be dried is left exposed to the sun for several days to achieve the desired moisture content. This is very common in developing countries where fuel is scarcely available to farmers due to high cost; open sun drying is the most popularly used method of drying since it is simple and only requires sunlight [56]. However, the major problems faced by open-air sun drying are insect infestation, dust and dirt contamination, long time for drying, overheating due to direct exposure, quality deterioration and low rate of transmission of heat due to condensation of the evaporated moisture [57]. In order to improve on the sun drying method, a simple form of solar dryer could be used to dry banana slices.

### *2.1.3 Indirect method*

Indirect solar drying involves the use of solar dryer to overcome the problems encountered by the direct method of drying. Different types of indirect solar dryers are chamber type, chimney type and wind-ventilated dryers. In the indirect method of solar drying, the heat acquired by the system is used to heat the air that flows through the product to be dried.

#### **2.2 Artificial drying methods**

#### *2.2.1 Convective drying*

Convective method of drying is used to remove water from banana through heat transfer in modern drying. Hot air is allowed to pass through the banana products in a manner to transfer the heat to the banana, and moisture is removed effectively [58].

Combination of osmotic and convective drying methods have been studied on many fruits and vegetables such as mango [59], mushrooms [60], ginger [61], jackfruit [62], button mushroom [63] and grapes [64], and these methods could be applied to drying of banana.

#### *2.2.2 Drying by radiation*

It has been discovered and reported that long drying time and high temperature are the factors responsible for the loss of heat-sensitive components of banana in traditional convective hot air drying. Drying by radiation is an alternative method that could be used to overcome the problems encountered in hot air drying. The use of electromagnetic radiation as in the case of microwave radiation is achieved through space by means of electric and magnetic fields. Microwave heating requires lesser amounts of time and temperature to remove moisture from banana slices [65]. One of the problems of microwave heating is due to low availability of water towards the end of the drying process. Radiation through microwave could be combined with other methods of drying such as vacuum drying which is an advantage over other methods [65]. Drying by radiation has been used to dry various agricultural produce including banana [66–68].

#### *2.2.3 Freeze-drying*

Freeze-drying uses the principles of moisture sublimation to remove from produce. Falade and Igbeka [69] have reported that the non-availability of liquid water during freezing and low temperature results in the production of a superior quality end product and most of the reactions involving the microbes are completely stopped. Freeze-drying method has several advantages over other drying methods in that its products have better rehydration property due to rapid drying and the organoleptic property of the rehydrated banana is almost the same with the fresh product [69]. Other benefits of freeze-drying method are as follows: freeze-dried products have minimum volume reduction, minute chemical change and minimum loss of volatile components [70]. However, freeze-drying is very expensive and uses more energy. Because of longer freeze-drying time, the product may collapse during drying which could lead to loss of aroma [71].

#### *2.2.4 Osmotic drying*

Osmotic drying involves the use of hypertonic solution; banana slices are placed in a hypertonic solution which causes a difference in concentration gradient and removal of water from banana to the solution. There is also diffusion of the solutes from the solution into the tissue of the banana slices [72]. The mass transfer which occurs during osmosis could be responsible for the change in physical, chemical and

**71**

*Banana Drying Kinetics*

cantly less [74].

*2.2.5 Hurdle technology*

in the final products [75].

taste, smell and texture.

safety of the products.

**2.3 Drying kinetics and modelling**

*DOI: http://dx.doi.org/10.5772/intechopen.84669*

nutritional values, taste and structural properties of the final products [62, 69, 73]. Osmotic active solutes include monosaccharides, disaccharides and salts such as sodium chloride. The major advantage of the process is that it could be conducted at room temperature since energy required for carrying out the procedure is signifi-

Hurdle technology is a method of ensuring that pathogens in banana fruits can be eliminated or controlled through the use of hurdles. This means the banana fruits will be safe for consumption and their shelf life will be extended. Hurdle technology usually works by combining several approaches thought of as 'hurdles' which the pathogen has to overcome if it is to remain active in banana flour. The right combination of hurdles can ensure that all pathogens are eliminated or rendered harmless

Leistner [77] defined hurdle technology as a planned application and combination of hurdles which eliminates or reduces the microbial load and makes dried banana safe and stable as well as improves or maintains the organoleptic and nutritional quality and the economic viability of dried banana. The organoleptic quality of the banana products refers to its sensory properties, which includes look,

Several combinations of hurdles are used in banana preservation. Examples of hurdles in a banana fruit system are high temperature during processing; low temperature during storage, increasing the acidity and lowering the water activity or redox potential; or the presence of preservatives. Alasalvar [76] reported that bananas are preserved according to the type of pathogens and how risky they are. The author reinstated that the intensity of the hurdles can be adjusted individually to meet consumer preferences in an economical way, without compromising the

Several hurdles are considered to be important in the preservation of various vegetables and fruits including banana to enhance their stability and shelf life. Shelf-stable grated carrot products are developed using hurdle technology.

The *drying kinetics* is used to describe the combined macroscopic and microscopic mechanisms of heat and mass transfer during *drying*, and it is affected by *drying* conditions, types of *dryer* and characteristics of materials to be *dried*. Studying drying kinetics is a means to choose appropriate drying methods and to control the processes of drying. It is also important for engineering and process optimization. Drying kinetics is used to show removal of moisture from products, and it has to do with process variables, and hence, a better understanding of drying rate will help in developing a drying rate model [78]. There are three drying models, namely, theoretical, semi-theoretical and empirical according to Khazae and Daneshmandi [79]. Theoretical models dealt with internal resistance in transfer of moisture, while semi-theoretical and empirical models worked on external resistance in the transfer of moisture between air and products [80]. Empirical model's main shortcoming is that it does not consider the basics of drying process but explains only the drying curve for drying conditions but not the processes that occur during drying [81]. Examples of semi-theoretical models are the Lewis

model, Henderson and Pabis model, Logarithmic model, Page model, etc.

The theoretical model that is commonly used in drying rate is Fick's second law of diffusion. Theoretical models have been found to be inadequate, tend to generate

#### *Banana Drying Kinetics DOI: http://dx.doi.org/10.5772/intechopen.84669*

nutritional values, taste and structural properties of the final products [62, 69, 73]. Osmotic active solutes include monosaccharides, disaccharides and salts such as sodium chloride. The major advantage of the process is that it could be conducted at room temperature since energy required for carrying out the procedure is significantly less [74].

## *2.2.5 Hurdle technology*

*Banana Nutrition - Function and Processing Kinetics*

through the product to be dried.

**2.2 Artificial drying methods**

applied to drying of banana.

agricultural produce including banana [66–68].

during drying which could lead to loss of aroma [71].

*2.2.2 Drying by radiation*

*2.2.3 Freeze-drying*

*2.2.4 Osmotic drying*

*2.2.1 Convective drying*

are chamber type, chimney type and wind-ventilated dryers. In the indirect method of solar drying, the heat acquired by the system is used to heat the air that flows

Convective method of drying is used to remove water from banana through heat transfer in modern drying. Hot air is allowed to pass through the banana products in a manner to transfer the heat to the banana, and moisture is removed effectively [58]. Combination of osmotic and convective drying methods have been studied on many fruits and vegetables such as mango [59], mushrooms [60], ginger [61], jackfruit [62], button mushroom [63] and grapes [64], and these methods could be

It has been discovered and reported that long drying time and high temperature are the factors responsible for the loss of heat-sensitive components of banana in traditional convective hot air drying. Drying by radiation is an alternative method that could be used to overcome the problems encountered in hot air drying. The use of electromagnetic radiation as in the case of microwave radiation is achieved through space by means of electric and magnetic fields. Microwave heating requires lesser amounts of time and temperature to remove moisture from banana slices [65]. One of the problems of microwave heating is due to low availability of water towards the end of the drying process. Radiation through microwave could be combined with other methods of drying such as vacuum drying which is an advantage over other methods [65]. Drying by radiation has been used to dry various

Freeze-drying uses the principles of moisture sublimation to remove from produce. Falade and Igbeka [69] have reported that the non-availability of liquid water during freezing and low temperature results in the production of a superior quality end product and most of the reactions involving the microbes are completely stopped. Freeze-drying method has several advantages over other drying methods in that its products have better rehydration property due to rapid drying and the organoleptic property of the rehydrated banana is almost the same with the fresh product [69]. Other benefits of freeze-drying method are as follows: freeze-dried products have minimum volume reduction, minute chemical change and minimum loss of volatile components [70]. However, freeze-drying is very expensive and uses more energy. Because of longer freeze-drying time, the product may collapse

Osmotic drying involves the use of hypertonic solution; banana slices are placed in a hypertonic solution which causes a difference in concentration gradient and removal of water from banana to the solution. There is also diffusion of the solutes from the solution into the tissue of the banana slices [72]. The mass transfer which occurs during osmosis could be responsible for the change in physical, chemical and

**70**

Hurdle technology is a method of ensuring that pathogens in banana fruits can be eliminated or controlled through the use of hurdles. This means the banana fruits will be safe for consumption and their shelf life will be extended. Hurdle technology usually works by combining several approaches thought of as 'hurdles' which the pathogen has to overcome if it is to remain active in banana flour. The right combination of hurdles can ensure that all pathogens are eliminated or rendered harmless in the final products [75].

Leistner [77] defined hurdle technology as a planned application and combination of hurdles which eliminates or reduces the microbial load and makes dried banana safe and stable as well as improves or maintains the organoleptic and nutritional quality and the economic viability of dried banana. The organoleptic quality of the banana products refers to its sensory properties, which includes look, taste, smell and texture.

Several combinations of hurdles are used in banana preservation. Examples of hurdles in a banana fruit system are high temperature during processing; low temperature during storage, increasing the acidity and lowering the water activity or redox potential; or the presence of preservatives. Alasalvar [76] reported that bananas are preserved according to the type of pathogens and how risky they are. The author reinstated that the intensity of the hurdles can be adjusted individually to meet consumer preferences in an economical way, without compromising the safety of the products.

Several hurdles are considered to be important in the preservation of various vegetables and fruits including banana to enhance their stability and shelf life. Shelf-stable grated carrot products are developed using hurdle technology.
